This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-071607, filed Mar. 17, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a semiconductor polishing apparatus and method for polishing films using chemical/mechanical methods to obtain a smooth surface. More specifically, the present invention relates to a CMP (Chemical/Mechanical Polishing) apparatus and method which allow measurements of the thickness of films in the middle of polishing.
One method to remove surface irregularities of a film deposited over the surface of semiconductor devices is CMP technology. The CMP is to polish the surface of a film using chemical/mechanical methods. In the CMP, for good control of the residual thickness of a film after polishing, there has been demand for knowledge of the film thickness in the middle of polishing.
FIG. 1 shows a prior art. For example, a wafer 103 in the middle of manufacturing process for semiconductor devices is placed on a polishing cloth 102 attached to the surface of a polishing platen 101. The wafer 103 is then held by a top ring 104 with the to-be-polished surface (in which a device is manufactured) down. At the time of polishing, the top ring 104 is rotated by a motor 116. The polishing platen 101 is rotated by a motor 115.
A film thickness measuring hole 105 is formed in the polishing platen 101 and the polishing cloth 102. A measuring radiation irradiation device 106 and a film thickness measuring instrument 107 are placed below the measuring hole 105 formed in the platen 101. At the time of measurement, the radiation irradiation device 106 emits visible light toward the film of the wafer 103. The measuring instrument 107 receives and analyzes reflected light from the film of the wafer 103 to measure the film thickness in the middle of polishing.
With this method, however, information (film thickness) can be obtained only from unspecified portions of the surface of the semiconductor device because the wafer 103 is rotating. Therefore, the thickness of specified portions of the film cannot be known accurately and difficulties are involved in controlling the residual thickness of the film.
Another method is to allow a wafer to protrude its portion from a polishing platen and direct visible light to that portion of the wafer. However, this method also has the problem that information can be obtained only from unspecified portions of the surface of the semiconductor device.
Thus, with the conventional methods, it is impossible to control strictly the amount by which the film is polished, which results in short or excessive polishing and consequently in the formation of form defects, such as dishing, thinning, and rounding.
In addition, analysis software to measure the film thickness is complex in processing. Thus, the instrument has to be tailored each time the analysis software is updated, making the apparatus management complex.
It is an object of the present invention to provide a semiconductor polishing apparatus and method which allow the residual thickness of a film to be polished in the surface of semiconductor devices manufactured on a wafer to be controlled well and provides ease of management.
According to an aspect of the present invention there is provided a semiconductor polishing apparatus comprising: a polishing platen to which a polishing cloth is attached; a wafer holder for holding a wafer so that a surface to be polished of it is opposite to the surface of the polishing cloth; a measuring radiation irradiation device for directing pulsed measuring radiation onto the surface to be polished of the wafer in the middle of polishing; a data processor for determining the pulse repetition rate of the measuring radiation emitted by the measuring radiation irradiation device; and a film thickness measuring device responsive to reflections of the pulsed measuring radiation from the surface to be polished of the wafer for measuring the thickness of a film to be polished present at the surface to be polished of the wafer.
According to another object of the present invention there is provided a semiconductor polishing method comprising the steps of: setting a surface to be polished of a wafer held by a wafer holder opposite to the surface of a polishing cloth attached to the surface of a polishing platen; supplying the surface of the polishing cloth with a polishing slurry; polishing a film present in the surface of the wafer by bring the surface of the polishing cloth and the surface of the wafer into contact with each other with a load applied to the wafer; irradiating the surface of the wafer with pulsed measuring radiation at the time of polishing from a measuring radiation irradiation device; determining the pulse repetition rate of the pulsed measuring radiation by a data processor; and measuring the thickness at a specified site of the film in the middle of polishing on the basis of reflections of the pulsed measuring radiation from the surface of the wafer by a film thickness measuring device.
According to still another aspect of the present invention there is provided a semiconductor polishing method comprising the steps of: setting a surface to be polished of a wafer held by a wafer holder opposite to the polishing surface of a polishing platen; rotating the polishing platen and the wafer holder by first and second motors, respectively; irradiating the surface of the wafer with pulsed measuring radiation at a pulse repetition rate calculated from the numbers of rotations of the first and second motors; and measuring the thickness of a specified portion of a film present in the surface of the wafer in the middle of polishing on the basis of reflections of the pulsed measuring radiation from the surface of the wafer.
The present invention allows the thickness of a specified portion of a film to be polished in the surface of semiconductor devices to be measured accurately. Thus, the amount by which a film is polished can be controlled strictly.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.